1. Field of the Invention
This invention relates to a thermally assisted magnetic head for writing of signals by a thermally assisted magnetic recording method.
2. Description of the Related Art
As the recording density of a hard disk drive becomes higher, a thin film magnetic head has been required to further improve its performance. One example of the thin film magnetic head is a composite type thin film magnetic head, which is widely used. The composite type thin film magnetic head has a structure in which a magnetic detecting element, such as a magnetoresistive (MR) effect element, and a magnetic recording element, such as an electromagnetic coil element, are stacked. The magnetic detecting element and the magnetic recording element are used to read and write data signals from and onto a magnetic disk that is a magnetic recording medium.
In general, the magnetic recording medium is a discontinuous body of fine magnetic particles aggregated, and each of the fine magnetic particles is made in a single magnetic domain structure. A recording bit is composed of a plurality of fine magnetic particles. Therefore, in order to increase the recording density, it is necessary to decrease the size of the fine magnetic particles and thereby decrease unevenness at borders of recording bits. However, the decrease in the size of the fine magnetic particles raises the problem of degradation of thermostability of magnetization due to a reduction in volume.
A measure of the thermostability of magnetization is given by Ku·V/kB·T. In this case, Ku represents the magnetic anisotropy energy of the fine magnetic particles, V represents the volume of one magnetic particle, kB represents the Boltzmann constant, and T represents absolute temperature. The decrease in the volume V of fine magnetic particles leads to decrease of Ku·V/kB·T and to degradation of the thermostability. A conceivable countermeasure to this problem is to increase the magnetic anisotropy energy Ku at the same time, but this increase of Ku will lead to increase in the coercive force of the recording medium. In contrast to it, the intensity of the writing magnetic field by the magnetic head is virtually determined by the saturation magnetic flux density of a soft magnetic material making the magnetic poles in the head. Therefore, the writing becomes infeasible if the coercive force exceeds a tolerance determined from this limit of writing magnetic field intensity.
As a method of solving this problem of thermostability of magnetization, a so-called thermally assisted magnetic recording method has been proposed in which, while a magnetic material with large magnetic anisotropy energy Ku is used, heat is applied to the recording medium immediately before application of the writing magnetic field, to decrease the coercive force, and writing is performed in that state. This method is generally classified into a magnetic dominant recording method and an optical dominant recording method. In the magnetic dominant recording method, the dominant of writing is an electromagnetic coil element and the radiation diameter of light is larger than the track width (recording width). On the other hand, in the optical dominant recording method, the dominant of writing is a light radiating portion and the radiation diameter of light is approximately equal to the track width (recording width). In other words, the magnetic field determines the spatial resolution in the magnetic dominant recording method, whereas the light determines the spatial resolution in the optical dominant recording method.
The structure of the thermally assisted magnetic head recording apparatus of this type is disclosed in which a light source, such as a semiconductor laser, is located at a position apart from a slider with a magnetic recording element for generating a magnetic field and in which light from this light source is guided through an optical fiber, a lens, etc., to a medium-facing surface of the slider in patent documents (International Publication No. WO92/02931 Pamphlet (Japanese Translation of International Application No. H06-500194), International Publication No. WO98/09284 Pamphlet, (Japanese Translation of International Application No. 2002-511176), Japanese Published Unexamined Patent Application No. H10-162444, International Publication No. WO99/53482 Pamphlet (Translation of International Application No. 2002-512725)) and a non-patent document (Shintaro Miyanishi et al., “Near-field Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, 2005, Vol. 41, No. 10, pp. 2817-2821).
Additionally, the thermally assisted magnetic head is disclosed in which the magnetic recording element and the light source are integrated on a side surface of the slider, and the thermally assisted magnetic head is disclosed in which the magnetic recording element and the light source are integrated on the medium-facing surface of the slider in patent documents (Japanese Published Unexamined Patent Application No. 2001-283404, Japanese Published Unexamined Patent Application No. 2001-325756, Japanese Published Unexamined Patent Application No. 2004-158067, Japanese Published Unexamined Patent Application No. 2004-303299) and a non-patent document (Keiji Shono and Mitsumasa Oshiki “Status and Problems of Thermally Assisted Magnetic Recording” Journal of the Magnetics Society of Japan, 2005, Vol. 29, No. 1, pp. 5-132).